Modern mobile communication techniques tend to provide multimedia services transmitted in high rates for users, as shown in FIG. 1. FIG. 1 is architecture of a long term evolution (LTE) system provided according to traditional art.
In FIG. 1, user equipment (UE) 101 is a terminal device configured to receive data. Evolved universal terrestrial radio access network (E-UTRAN) 102 is a radio access network which includes a macro base station (eNode B/Node B) to provide a radio network interface for the UE. Mobility management entity (MME) 103 is in charge of mobility context, session context, and security information of the UE. Serving gateway (SGW) 104 is mainly configured to provide a user plane function. The MME 103 and the SGW 104 may be located in a same physical entity. Packet data network gateway (PGW) 105 is in charge of functions such as charging and lawful interception, and it may be located in a same physical entity together with the SGW 104. Policy and charging rule function (PCRF) entity 106 provides quality of service (QoS) policy and charging rules. Serving general packet radio service (GPRS) support node (SGSN) 108 is a network node device that provides routing for data transmission in a universal mobile telecommunications system (UMTS). Home subscriber server (HSS) 109 is a home sub-system of the UE, and is responsible for protecting user information such as a current location of the UE, an address of a serving node, user security information, and packet data context of the UE.
The object of the group communication service is to provide a fast and efficient mechanism to distribute same data to UEs in a group. The idea of the group communication service has been widely used in land mobile radio (LMR) systems of public security organizations. A typical application is to provide a push to talk (PTT) function. When the group communication service is introduced into the LTE technique, the group communication service for LTE at least should support voice communications, and performance thereof should be equivalent to PTT performance of traditional group communication services. The group communication service for LTE should support a UE in different statuses and different environments where a UE is located. LTE has an ability of broadband data transmission, and the group communication service for LTE should support data communications such as voice and video communications.
Group call system enabler (GCSE) service for LTE is a service that introduces application layer functions into the 3GPP technique to support the group communication. UEs of a LTE system are divided into different GCSE groups, and a UE may belong to one or more different GCSE groups. In a GCSE group, a UE that needs to receive GCSE service data is called receiving group member, and a UE that needs to send GCSE service data is called sending group member. The GCSE service for LTE is communications between sending group members and receiving group members. The GCSE service for LTE also needs to support a UE communicating with multiple GCSE groups at the same time, e.g., the UE carrying out a voice service with a GCSE group and carrying out a video service or other data services with other GCSE groups.
To efficiently use air interface resources, for a service where multiple receiving UEs receive same data, the service may be provided to the receiving UEs by a broadcast mode and a multicast mode, i.e., the GCSE service for LTE being implemented by the broadcast mode and the multicast mode. This kind of broadcast and multicast service is referred to as multimedia broadcast and multicast service (MBMS). Each MBMS bearer provides services in its serving area, and for each cell in the serving area, uses a dedicated control channel, e.g. a multicast control channel (MCCH), to transmit MBMS signaling. LTE introduces a broadcast/multicast service center (BM-SC), a multi-cell/multicast coordination entity (MCE), and a MBMS gateway (MBMS-GW). The BM-SC is a multimedia broadcast-multicast service providing center, and MBMS data packets are sent from the BM-SC to the MBMS-GW. The MBMS-GW is a logic entity, and may be integrated into another entity or may be configured separately between the BM-SC and an eNB, responsible for sending/broadcasting MBMS data packets to each eNB which is to transmit data. Each eNB forwards the MBMS data packets to UEs. MBMS control signaling is sent from the BM-SC to the MBMS-GW, and then it is sent to an EUTRAN through a MME. A MCE is configured to receive MBMS signaling, decide to use a multimedia broadcast single frequency network (MBSFN) transmission mode, and transmit MBMS signaling to a corresponding eNB.
At present, when the MBMS is implemented in a LTE system, a continuous area is defined. In this continuous area, each eNB uses a same carrier to synchronously transmit same MBMS signaling, so as to improve MBMS receiving quality of UEs. This continuous area is called single frequency network (SFN) area. The SFN area contains a group of cells whose geographical locations are continuous. The group of cells uses a same radio resource to synchronously transmit a specific MBMS.